Internal combustion engines operating on the four-stroke principle have a lubrication system consisting of various passages inside the crankcase, cylinder block, and cylinder head assembly to lubricate the various components of the engine. On engines having a dry sump, the oil used for lubricating these components is stored in an oil tank. The oil flows from the oil tank to the passages and is returned to the oil tank from the passages after circulating though the engine.
The oil tank is generally in the form of a container that is separate from the engine. To permit oil to flow to and from the oil tank therefore requires various tubes or pipes to be connected between the oil tank and the engine. Installing these connections requires time during the assembly of the engine. Also, as would be understood, the more connections exist, the greater the likelihood of oil leaks. The oil tank, being a separate container, also needs to be installed in the vehicle where the engine is located, which can sometimes be difficult due to the lack of space in the vehicle, particularly in recreational vehicles such as snowmobiles or personal watercraft. Further increasing the difficulty in installing the oil tank in a vehicle is the importance, in relatively lightweight vehicles, to maintain a proper weight balance in the vehicle, which is the case in recreational vehicles. If a mass, such as the oil tank, is disposed in the wrong position, it could negatively affect the performance of the vehicle.
Therefore, there is a need for an internal combustion engine having an oil tank that does not require the above-mentioned connections and can be easily installed in a vehicle.
During the operation of the engine, some of the gases present in the combustion chambers pass through a gap between the pistons and the walls of the cylinders and enter the crankcase. These gases are known as blow-by gases. In the crankcase, the blow-by gases mix with oil droplets. The mixture of blow-by gases and oil droplets present in the crankcase is then returned to the oil tank.
Upon returning to the oil tank, some of the blow-by gases will separate from the oil and rise to the top of the oil tank. However, some of the blow-by gases may remain mixed with the oil. If the blow-by gases are recirculated with the oil in the passages of the lubrication system, they can become trapped in portions of the passages creating a “bubble” of blow-by gases. The portion of the engine where the bubble is located can become very hot since no oil flows in that portion of the passages, which could damage the engine.
Therefore there is a need to separate the blow-by gases from the oil prior to recirculating the oil in the passages of the lubrication system.
The blow-by gases that rise to the top of the oil tank need to be evacuated, otherwise pressure could build up inside the oil tank which could lead to oil leaking from the oil tank or even failure of the oil tank.
To address this problem, most oil tanks are provided with a blow-by gas outlet near or at the top portion thereof which communicates with the exterior of the engine (i.e. the environment or an air intake system of the engine). This outlet allows the blow-by gases to be vented to the exterior of the engine.
If for some reason, the vehicle in which the oil tank is disposed should become overturned, the oil needs to be prevented from leaking into the environment or the air intake system of the engine (as the case may be) via the blow-by gas outlet. This is usually achieved by providing a valve that closes upon detecting that the vehicle has overturned, thus preventing the oil from flowing to the environment or the air intake system of the engine. However, the valve could potentially fail or the sensor associated with the valve could not detect that the vehicle has overturned, which would lead to oil leaking into the environment or the air intake system of the engine. The sensor could also fail and cause the valve to close even though the vehicle did not overturn, which could lead to pressure build-ups inside the oil tank. Also, a valve, and its associated sensor, add cost to the manufacturing of the engine and oil tank and require additional assembly.
Therefore, there is a need to prevent oil from leaking into the environment or the air intake system of the engine when the vehicle in which the oil tank is located becomes overturned without requiring a valve.
Also, when a vehicle such as a snowmobile or all-terrain vehicle goes up or down a hill, or a vehicle such as a personal watercraft or a motorcycle takes a sharp turn, the vehicle becomes angled relative to horizontal, and if that angle is large enough, it may cause the oil in the oil tank to block the blow-by gas outlet. The blow-by gas outlet, being located at or near the top of the oil tank, also becomes blocked when the vehicle overturns. However, the blow-by gases still need to be vented under those conditions.
Therefore, there is a need for an oil tank that can vent blow-by gases even though the blow-by gas outlet becomes blocked by the oil in the oil tank due to the oil tank being angled relative to horizontal or being overturned.